[Elecraft] 270 foot (ish) Doublet & K3 ATU

[Rick Bates]

Sure it does, you're changing the line losses, tweaking C and L and therefore the SWR (always measured at the tuner, but moving peaks and valleys closer/further away from that point) any time you alter the system.

There are specific resonant points in an antenna system (typically each half wavelength).  The goal is to make one of them at the radio.  In a multiband antenna, this is um, challenging if not impossible. 

The common mode choke stops any into the shack, but what is varying is the coax from rig to choke.  Those losses change and resonant portions of the feed system change so I'd expect to see the tuning change. 

The odd part is no major difference from 70' of window line to 100'.   My presumption is that the antenna is simply too close to dirt, so changes are more subtle or masked. 

The coax portion (if used) should be as short as feasible to keep line losses low.  If you can't, you'll have to accept the losses; sometimes I use 35' instead of 10' so I can be more effective (get a better tune) on the bottom of 80M and run the amp.  Signal loss is not as significant there and receiver gain is far more than ample.   I won't do that on 10M where the loss is major (2-3 S units).

It's a system, not just a bunch of pieces.  They all add up. 

FWIW, 170' per leg of the dipole is 5/8 wave mid 75 meters; not a resonant antenna.  It requires a tuner. 

If the OP has time and the space, an intriguing option is the 160 full wave loop.  It resonates in every ham band or close enough.  Only the 160 M loop does this, an 80 M loop does not.  I don't have the real estate, or tall trees. 

So for field day, a meadow with enough tall trees on the edge... Hmmm...

73,
Rick wa6nhc

Tiny iPhone 5 keypad, typos are inevitable

> On May 15, 2014, at 1:33 PM, "Wes (N7WS)" <wes at triconet.org> wrote:
> 
> This makes no logical sense, unless you have a big common-mode problem.
> 
> Wes  N7WS
> 
> 
> 
>> On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
>> Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.
> 
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